Social factors play a major role in alcohol use and dependence, but researchers rarely study the effects of alcohol in group settings. This project will systematically measure the effects of alcohol on positive and negative affect and social bonding during initial group formation, and determine if persons with personality traits posing a risk for alcoholism are more sensitive to these effects. Presumably, if such persons find effects of alcohol to be more rewarding, they will become more likely to rely on alcohol to regulate affect. Many of these traits are inherently social (e.g., extroversion), and this will be the first study to test their impact on the effects of alcohol in a social setting. Seven-hundred-twenty social drinkers will be assembled into 240 three-person groups of strangers (all female groups, groups with one male and two females, groups with two males and one female, and all male groups). All members of each group will drink over 30-min a moderate dose of alcohol (males: 0.82 g/kg;females: 0.74 g/kg), a placebo, or a nonalcoholic control drink. This group drinking period will be recorded using a digital control system that synchronizes multiple streams of video as interactions unfold over time. This system enables precise analysis of the duration and sequence of selected facial expressions and speech behaviors. The project will be informed by (a) social psychological theory and research on small groups, (b) advances in the systematic measurement of observed behavior, and (c) multi-level statistical modeling techniques that account for the nonindependence of group members. We will assess a variety of individual-level responses, including facial expressions related to positive and negative affect using Ekman et al's (2002) Facial Action Coding System. We also will assess a range of group-level responses, including coordination of smiling and speech behaviors. We predict that the belief that one has consumed alcohol will enhance positive affect, reduce negative affect (e.g., social anxiety), and facilitate social bonding during initial group formation (i.e., a placebo effect). Further, we predict that actual alcohol consumption will enhance social bonding processes beyond what is found with a placebo beverage. This study will be the first with sufficient power to comprehensively examine the moderating roles of gender and personality traits on the reinforcing effects of alcohol in groups. Regardless of the outcome, the study will provide critical data regarding observable effects of alcohol on social drinkers that will help illuminate the social and emotional determinants of drinking patterns and problems for men and women.